(19)
(11) EP 0 426 632 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
18.09.1991 Bulletin 1991/38

(43) Date of publication A2:
08.05.1991 Bulletin 1991/19

(21) Application number: 90850351.9

(22) Date of filing: 22.10.1990
(51) International Patent Classification (IPC)5F16J 9/00, B25D 11/12, B25D 17/06
(84) Designated Contracting States:
CH DE FR GB LI

(30) Priority: 28.10.1989 SE 8903623

(71) Applicant: Atlas Copco Berema Aktiebolag
S-131 24 Nacka (SE)

(72) Inventor:
  • Elvingsson, Bengt Albert Paul
    S-393 51 Kalmar (SE)

(74) Representative: Molin, Alexis 
Saltsjö Patentanalys AB, Tranbärsvägen 11
S-133 34 Saltsjöbaden
S-133 34 Saltsjöbaden (SE)


(56) References cited: : 
   
       


    (54) Impact motor


    (57) An impact motor comprises a housing (10) with a cylin­der (11) therein, in which a reciprocating drive piston (40) via a gas cushion in a working chamber (44) of said cylinder (11) repeatedly drives a hammer piston (15) to impact on and to return from the neck (17) of a tool (20) carried by the machine housing (10). A piston groove (68) is provided adja­cent to the front face (70) of the drive piston (40) and the peripheral part of said face (70) is rounded (71) towards said groove (68). A piston ring (41) is of steel having a temperature expansion coefficient substantially equal to the cylinder's (11) and is ground circumferentially to have a close sliding and sealing fit in the cylinder (11). The round­ed (71) drive piston face (70) is adapted to the inner diame­ter of said ring (41) so as to permit the ring (41) to be forced into said groove (68) undeformed to ride on a elasti­cally centering O-ring (69) of heat resistant rubber. The hammer piston (15) can alternatively have a similarly ar­ranged steel or heat resistant plastics material piston ring (16) therearound or be machined to a sliding and sealing fit in the cylinder (11).







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